Gold Miner $4
+1 action
+1 buy
You may gain a copper to your hand
If 1 supply pile is empty, you may gain a silver to your hand instead
If 2 supply pile is empty, you may gain a gold to your hand instead
Until first pile be empty, Candlestick Maker is virtually strictly better than it (except edge cases, like Bank).
Have you seen the City. That one goes from the worst village to the best laboratory.
Now I also wonder when I would pick it. A buy in an engine is never wrong. Would you buy it if you expect 1 pile going out fast... maybe. Defintly if you could upgrade it immidialty with another card. If you get attacked a lot, burn down a pile and get silver to keep roling. And if you expect that 2 piles will be empty quickly you would by it.
The question is, are there enough edge cases that you can make it work. I don't know yet.
You can at least stack Cities as a makeshift village before they become labs. Gold Miner feels it's only useful in a slog, buying it when the curses are about to run out. It's really a non-terminal silver that gains silvers, not exactly amazing, and when you're gaining Golds it's a bit too late in the game to use them anyway.
Can it go to $3? I think it's too weak at $4 but it might be more interesting at that price point.
$3 would be better. Changed the wording also a bit and changed they buy into a card
Gold Miner $3
+1 action
+1 card
You may take one of the following cards in hand:
a Copper
a Silver if 1 supply pile is empty
a Gold if 2 supply piles are empty.
I think that change would be better. Without support card you get the choice: "Would I delude my deck for just that 1 cash I need now...".
It still draws you out of a sloth, helps with alternate VP like gardens and Feadoms, and helps if you have a little too much to trash with cards like catapult or improve.